Control system



AJune 24, 1930. 4[ DAvls 1,768,122

- CONTROL SYSTEM f Original Filed Oct. 2.9, 1925 2 Sheets-Sheet l L Q msNvEN'row VBY mm ATTORNEY June 24, 1930. L. 1. DAVIS 1,768,122`

1 CONTROL SYSTEM Original Filed Oct. 29, 1925 2 Sheets-Sheet 2 DIZO U55-L/37 U34 ARnATuQE VaLTAGE ARMA Tune VDL-maf Flo FIEL o VoLTA GE NVENTOR'ATTORNEY Patented June 24, 1930 UNITED STATES PATENT OFFICE LEE I.Davis, or NEW YoEx, N. Y., AssmNort 'ro o'rrs ELEvA'roE. COMPANY, or

JERSEY CITY, NEW'JEESEY, A coRPoRATIoN or NEW JERSEY 'coNraoL SYSTEMOriginal application filed October 29,1925, Serial No. 65,612. Dividedand this application filed April '21, 1928. Serial No. 271,953. y

The invention relates to control systems, and particularly to controlsystems for elevators.

This application is a division of application Serial No. 65,612, filedOctober 29, 1925.

In elevator control systems where the elevator motor is supplied withcurrent vby a variable voltage generator, the ener'ator is required tooperate over a wi e range of E. M. F. values varying from a maximum inone direction to a maximum in the other. Where self-levelling apparatusis employed, the generator is re uired to operate at low values of E. inbringing the car to a level with a desired landing. Due to the residualflux of the generator field, the E. M. F. values obtained for a givenvalue of field current duringthe levelling operation vary considerably,depending on the previous magnetic state of the machine and whether thecar is approaching the landing or returning to the landin after anoverrun. Such variations in n. M. F. Values cause undesirable variationsin the voperation of the car during the levelling period.`

One feature of the invention resides in energizing the field' Windin ofa generator in such manner that the e ects of residual flux areminimized during periods vwhen a low voltage is desired.

Other features and advantages will become apparent vfrom the followingdescription,l

taken in connection with the accompanying drawings wherein oneembodiment of the invention is illustrated and in which:

Figure 1 is a diagram of an elevator control system;

Figure 2 is a fragmental schematic view of a portion of the elevatorsystem, illustrating the manner in which the generator field windingsare controlled during the levelling operation; and

Figures 3, 4 and 5 are hysteresis curves employed to illustrate theinvention.

No attempt is made in Figure 1 to show the coils and'contacts of thevarious electromagnetic switches in their associated positions, astraight diagram being employed wherein the coils and contacts of thevarious switches are separated in such manner as to` render the circuitsinvolved relatively simple. Alsov the parts of other switches andapparatus are separated in the interest of sim 1 ifying the diagram. Fora clearer un erstanding of the inventiomthe stationary contacts' of theswitchesl are illustrated incross section. It is to be understood thatthe system illustrated is chosen merely forfconvenience of descriptionand that, although described in conjunction Ywith a car switchcontrolled system, the invention is equally applicable to othertypesofelevator systems such as push button controlsystems and to othersystems employing a work motor supplied withcurrent from thefgeneratoryof a motor generator'set.

The motor generator sety comprlses a drivi,

ing motor 11, illustratedfor convenience of description as of the directcurrent type, and a variable voltage direct current generator 12. Thearmature of the driving motor is designated 13 and its field winding 14.-The armature ofthe generator is designated 15, itsseries field winding16, its'separately excited field winding being divided into two portions17 and 18. The elevator motor is designated as a whole by the numeral20, its armature being designated 21 and its fleld winding 22. Anadjustable resistance 29 is arranged in shunt vto the generator seriesfield Winding. Discharge resistances 23 and 24 are provided forl theportions 17 and 18 respectively ofthe generator separately excited fieldwinding. Discharge resistance 25 provided for the elevator motor fieldwinding. A resistance 26 is provided for controlling the strength of thegenerator field and therefore the voltage applied to the elevator motorarmature. 27 is the release coil forv the elevator motor electromagneticbrake. This coil is provided with discharge resistances 28, 30 and 31for controlling the application of the brake under different conditionsof operation. 32 and 33 are the up slow speed contacts and the downslowrspeed contacts respectively of the levelling switch, the up anddown fast speed levelling switch contacts being designated 34 and 35respectively. 36 is the armature and 37 `is-the--field windi of themotor 38 for moving the rollers x(ithe levelling switchinto position toclear the levelling cams. and 41 are the direct current supply mains. 42is a double pole knife switch for connecting the system to the supplymains. In order to suit the type of diagram employed, the blades of thisswitch are shown separated. The car switch is designated as a whole bythe numeral 43. 44 is the safety switch in the car. The various safety,limit, stop and emergency switches and door and gate contacts areomitted in order to simplify the description.

The electromagnetic switches have been designated as follows:

A-Potential switch,

B-Up direct-ion switch,

C-Down direction switch,

D-Up slow speed levelling relay,

E-Down slow speed levelling relay,

F-Accelerating switch,

(ir-Maintaining relay,

H-Brake switch,

J-Protective relay,

K-AuXiliary protective relay,

L-Slow down switch,

M-Series field relay,

N-Series field switch,

G-Hard brake switch,

P-Levelling switch motor relay.

Throughout the description which follows, these letters, in addition tothe usual reference numerals, will be applied to the parts of the aboveenumerated switches. For example, contacts B 66 are contacts on the updirection switch, while actuating coil A 45 is the coil that operatesthe potential switch. The electromagnetic switches are shown .in theirdeenergized positions.

Upon the closing of the knife switch 42, the driving motor 11, elevatormotor field winding 22 and potential switch actuating coil A 45 areenergized, the circuit for coil A 45 being by way of line 46 includingprotective relay contacts J 47, auxiliary protective relay contacts K 48and safety switch 44. The driving motor starts in operation, bringingthe generator 12 up to full speed. Starting means for the drivin motorare omitted to simplify the description. The potential switch, uponoperation, causes the engagement of contacts A and A 51 preparing thecircuit for the generator separately excited field winding, theelectromagnetic brake release coil and the control circuits. Thecondition of the circuits so far described might be termed normal.

Assume that the system is designed for an installation of several floorsand that the car is at rest at the first floor landing. In order tostart the car in the up direction, the operator moves the car switchinto position where its contact bar 52 bridges contacts 53, 54,' 55 and56. Upon the contact bar 52 engaging contact 54, a circuit is completedfor the actuating coil B 57 of the up direction switch and the actuatingcoil H 58 of the brake switch. This circuit may be traced from theleft-hand blade of switch 42, by way of line 79 through contacts A 50,by way of line 60 through coils H 58 and B 57, contacts 54 and 53 of thecar switch, by way of line 61 through contacts C 62, line 63, switch 44,line 46, by way of line 89, to the right-hand blade of switch 42. Theengagement of the contact bar and contact 55 prepares a circuit for theactuating coil F 83 of the accelerating switch. The engagement of thecontact bar and contact 56 completes a circuit for the actuating coil P59 of the levelling switch motor relay. This circuit may be traced fromthe lefthand blade of switch 42, by way of line 79 through contact A 50,by way of line 92 through coil P 59, contacts 56 and 53 of the carswitch, to the right-hand blade of switch 42 as above traced.

It is preferred to provide the direction switches with a mechanicalinterlock to pre- Vent their simultaneous operation. Such an interlockmay be of the form of a walking beam pivotally mounted for engagingcatches on the armatures of the direction switches. Upon operation ofthe up direction switch in response to the energization of its actuatingcoil B 57, contacts B 65 separate and contacts B 66, B 67 and B 68engage. The separation of contacts B 65 breaks the circuit leading fromthe car switch down feed Contact 70, contacts B 65 and the correspondingdown direction switch contacts C 62 serving as electrical interlocks.The engagement of contacts B 68 prepares the circuit for the updirection switch holding coil B 71 and the brake switch holding coil H72. The engagement of contacts B 66 and B 67 completes a circuit for thegenerator separatelyI excited field winding. This circuit may be tracedfrom the left-hand blade of switch 42, by way of line 79 throughcontacts A 50 and resistance 26, by way of line 7 3 through contacts B66, by way of line 74 through field winding portion 17, actuating coil G75 of the maintaining relay, slow-down switch contacts L 76, fieldwinding portion 18, by way of line 89 through contacts B 67 and contactsA 51, to the right-hand blade of switch 42. Relay G does not operate atthis time as insuicient current is supplied to its actuating coil.

The brake switch H operates simultaneously with the direction switch B.Switch H. upon operation. causes the separation of contacts H 77 and H78 and the engagement of contacts H 80 and H 81. The separation ofcontacts H 77 disconnects the generator separately excited field windingfrom the generator armature. The purpose of contacts H 77 will be seenfrom later' description. The separation of contacts H 78 disconnectsresistance 31 from across the brake release coil 27. Resistance 81 beingof low ohmic value, its disconnection before contacts H 8O engageprevents excess power consumption from mains 40 and 41. The engagementof contacts H 80 completes the circuit for the brake release coil 27.This circuit may be traced from the left-hand blade of switch 42, by wayof line 79 through contacts A 50, by way of line 82 through coil 27 andcontacts H 80, by way of line 89 through contacts A 51, to theright-hand 4blade of switch 42. The engagement of contacts H 81completes the circuit for the accelerating switch actuating coil F 83.This circuit may be traced from the left-hand blade of switch 42, by wayof line 79 through contacts A 50, by way of line 84 through contacts H81, reactance 85 and coil F 83, contacts 55 and 53 of the car switch, byway o1 11ne 61 through contacts C 62, line 63, switch 44, line 46, line89, to the right-hand blade of switch 42.

The levelling switch motor relay, upon operation, causes the engagementof contacts P 93, completing the circuit for the levelling switch motor38. This circuit may be traced from the left-hand blade of switch 42, byway of line 79 through contacts A 50, by way of line 94 through armature36 and field winding 37 of motor 38 and contacts P 93, by way of'line 89through contacts A 51, to the righthand blade of switch 42. Thelevelling switch motor acts to move the levelling switch operatingrollers so as to clear the levelling cams during movement of the car.This operation will be explained later.

The brake release coil 27 being energized and current being suppliedfrom the generator armature 15 to the elevator motor armature 21, due tothe generator field windlng portions 17 and 18 being energized, theelevator motor starts. The field winding portion 18 as now connectedassists the field winding portion 17.

The accelerating switch F does not operate immediately the circuitforits actuating coil F 83 is completed, its action being delayed by thereactance 85. Upon operation, switch F causes the separation of contactsF 8'( and the engagement of contacts F 88 and F 90. The separation ofcontacts F 87 removes t-ne short-circuit around the holding coil P 91 ofthe levelling switch motor relay. The engagement of contacts F 88completes the circuit for holding coils B 71, P 91 and H 72. Thiscircuit may be traced from the lefthand bladeof switch 42, by way ofline 79 through contacts A 50, by way of line 95 through coil B 71 andcontacts B 68, by way of line 96 through coils P 91 and H 72 andcontacts F 88, by way of line 89 through contacts A 51, to theright-hand blade of switch 42. The purpose of the energization of theseholding coils will be seen from later description. The engagement ofcontacts F 90 shortcircuits resistance 26, increasing the voltage comesup to full speed. Also sufficient current is now supplied to the coil Gto cause the operation of the maintaining relay.

Thus contacts G 97 engage, by-passing accelerating switch contacts F 88.It is to be understood that several. accelerating switches may beemployed to short-circuit successively sections of resistance 26, allbut one, illustrated as short-circuiting the whole of the resistance,being omitted in order to simplify' the description.

The starting of the car in the down direction is accomplished in asimilar manner and will be only briefly described. The operator movesthe car switch into position where its contact bar 52 bridges contacts70, 98, 100 and 101. Upon the engagement of the contact bar and contact98, a circuit is completed for the down direction switch actuating coilC 102 and coil H 58 which circuit may be traced from the left-hand bladeof switch 42, through coil H 58, as previously traced, by way of line103 through coil C 102, car switch contacts 98 and 70, by way of line 63through contacts B 65, to the right-hand blade of switch 42 aspreviously traced. The engagement of the contact bar and contact 10()prepares a circuit for coil F 83 and the engagement of the contact barand contact 101 completes a circuit for the coil P 59 by way of line104. The down direction switch, upon operation, causes the separation ofcontacts C 62 and the engagement of contacts C 105,v C 106 and C 107,these contacts corresponding with up direction switch contacts B 65, B66, B 67 and B 68 respectively. The holding coil of the down directionswitch is designated C 64. The circuit for coil F 83 is completed bycontacts H 81 as before. Further than this, the operation of startingthe car in the downdirection is the same as described for starting it inthe up direction.

Assume that the car is running in the up direction and that the operatorcenters the car switch between the second and third floors in ordertostop at the third Hoor landing. Upon the disengagement of the contactbar 52 and contact 56,'the circuit for the levelling switch motor relayactuating coil P 59 is broken. The relay remains in operated condition,however, due to its holding coil P 91. The disengagement of contact 55and the contact bar breaks the circuit for the accelerating switchactuating coil F 83. The accelerating switch,ltherefore, drops out,causing the separation of contacts F 88 and F 90 and the engagement ofcontacts F 87. The separation of contacts F 88 is simply in perparationfor the next starting operation, the circuit for coils B 71, P 91 and H72 being maintained by contacts G 97. The separation of contacts F 90removes the short circuit for resistance 26, decreasing the strength `ofthe generator field winding portions 17 and 18. Thus the generator E. M.F. is decreased and the speed of the elevator motor is reduced.Discharge resistances 23 and 24 act to smooth out the retardation. Theengagement of contacts F 87 short-circuits the holding coil P 91 of thelevelling switch motor relay. The disengagement of contact 54 andcontact bar 52 breaks the circuit for actuating coils B 57 and H 58. Theup direction switch and brake switch are maintained ih operatedcondition, however, by their holding coils B 71 and H 72 respectively.

The levelling switch motor relay P, dropping out upon theshort-circuiting of coil P 91, causes the separation of contacts P 93 todeenergize the levelling switch motor 38. In this manner the operatingrollers of the levelling switch are extended for engagement by the.levelling cams. Referring briefly to Figure 2, the levelling switchmotor is operatively connected to the levelling switch by means of anarm 108 on the motor shaft, a connecting link 110 and a lever 111. Inthe starting operation, the motor 38 being energized, arm 108 rotates,acting through link 110 and lever 111 to move the levelling switch as awhole about a pivot. In this manner the levelling switch operatingrollers 112 and 113 are moved into position where they do not engage thelevelling cams 114 and 115 during motion of the car, a stop beingprovided to determine the extent of the movement. It is to be understoodthat levelling cams are provided for each floor. The level- .ling switchis pivoted on a bracket 116 secured to the car frame. In the stoppingoperation, upon the deenergization of the levelling switch motor, aspring (not shown) moves the lever 111 and therefore the level'- lingswitch back into the first described position with the rollers 112 and113 extended for engagement by the levelling cams. Each pair oflevelling contacts 32, 33, 34 and 35 comprises a. stationary contact anda movable contact operated by the engagement of its corresponding rollerand levelling cam. The fast speed contacts 34 and 35 are arranged toseparate before their corresponding slow speed contacts 32 and 33 in thelevelling operation. Springs (not shown) are provided for causing theseparation of the contacts of the pairs as the levelling operation iseffected and stops are provided for determining the extent of movementof the rollers as they ride off the levelling cams.

t will be assumed that 'the up levelling switch operating roller 112moves onto the vertical surface of up levelling cam 114 before relay Gdrops out. The engagement of up slow speed levelling contact-s 32completes a circuit for actuating coils H 58 and B 57 and up slow speedlevelling relay actuating coil I) 117. This circuit may be traced fromthe left-hand blade of switch 42, by way of line 79 through contacts A50, by way of line 60 through coil H 58, coil B 57, contacts 32 and coilD 117, by way of line 89 through contacts A 51, to the right-hand bladeof switch 42. The engagement of fast speed levelling contacts 34by-passes resistance 118, the purpose of which will be explained below.The energization of coils H 58 and B 57 has no particular effect at thistime as the up direction switch and brake switch are being maintained inoperated condition by coils B 71 and H 72. Relay G, however, drops outas soon as the current flowing through its actuating coil drops to apredetermined value, the current being sustained by the action of fieldwinding portion 17 and discharge resistance 23. As a result, contacts G97 separate, deenergizing holding coils B 71 and H 72. The up directionswitch and brake switch are then maintained operated by coils B 57 and H58. Had the slow speed levelling contacts not been in engagement whenthe relay G dropped out, their subsequent engagement as roller 112 rodeonto the vertical surface of the cam would cause the energization ofcoils H 58 and B 57.

As set forth above, actuating coil D 117 of the up slow speed levellingrelay was energized upon the engagement of slow speed levelling contacts32. This relay, upon operation, causes the engagement of contacts D 120,completing the circuit for coil L 121. This circuit may be traced fromthe left-hand blade of switch 42, by way of line 79 through contacts A50, by way of line 122 through contacts D 120, up series field relayactuating coil M 123, up hard brake switch actuating coil O 124 and aportion 125 of reactance 126, by way of line 127 through coil L 121,line 128, by Way of line 89 through contacts A 51, to the right-handblade of switch 42. The circuit comprising contacts L 130, down seriesfield relay actuating'coil M 131, down hard brake switch actuating coilO 132 and the other portion 133 of reactance 126 are in parallel withcoils M 123 and O 124 and reactance portion 125. The polarities of thecoils of relay M and switch O and of the portions of the reactance 126is such that the ampere turns in coils M 131 and O 132 and reactanceportion'133 neutralize the ampere turns in coils M 123 and O 124 andreactancc portion 125 respectively so that the resultant ma gnetizingforce for the magnetic circuits of the relay, switch and reactance iszero. Thus neither relay M nor switch O operates. The slow-down switchL, however, operates immediately, causing the separation of contacts L76 and L 130 and the engagement of contacts L 134, L 135, L 136, L 137and L 138. The separation of contacts L 76 disconnects field windingportions 17 and 18, field winding portion 17 being connected to themains 40 and 41 by the engagement of contacts L 134 and field windingportion 18 being connected to the generator armature through resistance140 by the engagement of contacts L 135. The polarity of the latterconnection is such that the current supplied to the field windingportion 18 flows in such direction as to create a niagnetizing forcewhich opposes the magnetizing force due to field winding portion 17. Theeffect of field winding portion 18 is reduced by resistance 140. Theengagement of contacts L 138 completes a shortcircuit through fast speedlevelling switch contacts 34 for an adjustable portion of resistance 26.These connections cause the elevator motor to run at a desired levellingspeed as will be explained later in more detail. Resistances 23 and 24act to smooth out the changes in generator E. M. F. due to theseoperations. The purpose of the engagement of contacts L 136 and L 137will be explained later. It is to be noted that the separation ofcontacts L 76 also breaks the circuit for coil G 75. Thus had thecurrent in coil G not dropped to a sufficiently low value to permitrelay G to drop out, as might result from the late centering of the carswitch, the disengagement of contacts L 76 in response to the engagementof up slow speed levelling contacts 32 insures the separation ofcontacts G 97 and the cons uent deenergization of holding coils B 71 and72.

The separation of contacts L 130 breaks the parallel circuit aroundcoils M 123 and O 124 and reactance rportion 126. Upon the separation ofcontacts L 130, the reactance reduces the current su plied to coils M123 and O 124 to a value below that required to operate relay M andswitch O and thereafter prevents the ra id building up of the current,thus slightly elaying the operation of the rela and switch. Switch O maybe adjusted so that it operates almost immediately the current againststarts to build up. Switch O, upon operation, causes the separation ofcontacts O 141 to break the circuit for resistance 3() irl parallel withthe brake release coil 27. Relay M, upon operation, causes theengagement of contacts M 142 to complete the circuit for the seriesfield switch actuating coil N 143. This circuit may be traced from theleft-hand blade of switch 42, by way of line 79 through contacts A 50,by way of line 128 throu h coil N 143 and contacts M 142, by way o line89 through contacts A 51, to the right-hand blade of switch 42. SwitchN, upon operation, causes the separation of contacts N 144, breaking thecircuit including resistance 29 in shunt to the generator series fieldwinding 16. The generator series field coils are so wound' that, withoutthe parallel resistance 29, they would have too great an effect forproper operation of the car. The desired compoun vg is obtained byemploying the low resistance shunt. Upon separation of contacts N 144,vthe strength of the series field is increased for the levellingoperation so as to aid in obtaining the desired 'stopping operation. Theshort delay in the action of relay M, and therefore the switch N, uponthe initiation of the levelling operation, is desirable in order thatthe current in the generator armature-elevator motor armature circuitmay ad'ust itself to such a value that proper series eld strength duringthe levelling operation may be obtained.

As the car nears the third floor landing,

roller 112 rides offy the vertical surface onto the oblique surface ofcam 114. This results in theseparation of up fast speed levellingcontacts 34, removing the short-circuit around resistance 118. Thegenerator E. M. F., therefore, is again lowered and the elevator motorruns at its slowest speed.

Shortly before the car reaches an exact level with the landing, theroller 112 rides off the oblique surface of cam 114, thereby separatingthe slow speed levelling contacts 32. The circuit for coils H 58, B 57and D 117 is thus broken. Switch B drops out causing the separation ofcontacts B 68, B 67 and B 66 and the reengagement of contacts B 65. Thereengagement of contacts B 65 and the separation of contacts B 68 are inpreparation for the next starting operation. Contacts B 66 and B 67 willbe referred to later. Up slow speed levelling relay D drops out, causingthe separation of contacts D 120. Thus the circuit is broken for coils M123, O 124 and L 121. Relay M and switch L drop out immediately butswitch O is delayed in its action by the effect of reactance 126 anddischarge resistance 145. It is to be noted that the discharge currentfor coil O 124 and the reactance passes through down coil O 132 in suchdirection as to cause coil O 132 to assist coil O 124 inmaintainingswitch O in operated condition. Relay M, upon dropping out, causes theseparation of contacts M 142, deenergizing series field switch actuatingcoil N 143. Switch N drops out to reconnect resistance 29 across thegenerator series field. Switch L, upon droppin out, causes theseparation of contacts L 134, L 135, L 136, L 137 and L 138 and theengagement of contacts L 76 and L 130. The separation of contacts L 136,L 137 and L 138 and the engagement of contacts L 130 are in preparationfor the next starting operation. Contacts L 134, L 135 and L 76 will bereferred to later. Switch H drops out along with switch B and relay D,causing the separation of contacts H 81 and H 80 and the engagement ofcontacts H 78 and H 77. The separation of contacts H 81 is inpreparation for the next starting operation. The separation of contactsH 8O breaks the circuit for the brake release coil 27, effecting theapplication of the brake. The engagement of contacts H 78 during thisoperation has no particular function.

The engagement of contacts H 77 along with the separtion of contacts B66 and B 67 of the up direction switch and the separation of contacts L134 and L 135 and the engagement of contacts L 7 6 of the slowedownswitch disconnects field winding portion 17 from mains 40-41 andconnects both field winding portions 17 and 18 to the generatorarmature. The polarity of the latter connection is such that thegenerator sends current through the whole field winding in suchdirection as to oppose the flux which produces the generator E. M. F.,thus tending t0 destroy the residual flux of the generator field. Thus,the brake being applied and the generator separatel excited eld windingbeing disconnected rom mains 40-41, the car is brought to rest levelwith the third fioor landing. Since the engagement of contacts O 141 isdelayed, a hard application of the brake is obtained, assuring apositive stop at the landing.

In the event of an overrun, the operation of the switches is modified.Assuming in the above example that the car overruns the third fioor tothe extent of causing the engagement of down slow Speed levellingcontacts 33, a circuit is completed for coils H 58 and C 102 andactuating coil E 146 of the down slow speed levelling relay. Thiscircuit may be traced through coil H 58 as previously traced, by way ofline 103 through coil C 102, contacts 33 and coil E 146, by way of line89 through contacts A 51, to the righthand blade of switch 42. The relayE, upon peration, causes the engagement of contacts 147, completing acircuit for down, coils M 131 and O 132 and coil L 121. This circuit maybe traced from the left-hand blade of switch 42, by way of line 79through contacts A 50, by way of line 148 through contacts E 147, coilsM 131 and O 132 and reactance portion 133, by way of line 127 throughcoil L 121, to the right-hand blade of switch 42 as previously traced.Due to the fact that contacts L 130 are in engagement, up coils M 123and O 124 are connected in parallel with down coils M 131 and() 132.Thus, as previously explained, the switch L operates immediately,causing the separation of contacts L 130 and L 76 and the engagement ofcontacts L 134, L 135, L 136, L 137 and L 138. Since contacts H 77 areseparated and contacts C 105 and C 106 are in engagement due to theenergization of coils H 58 and C 102 respectively, the separation ofcontacts L 76 and the engagement of contacts L 134 and L 135 cause theconnection of field winding portion 17 to mains 40-41 and the connectionof field winding portion 18 to the generator armature. As will be seenromlater description, such connections of the field winding portionscause the generationl of an E. M. F. which causes the elevator motor tobe returned to the floor in the down direction and which E. M. F. is ofa value very near to that generated with the car approaching the floorin the up direction. Variations in the generator E. M. F. for thelevelling operations cause variations in the operation of the elevatormotor. By causing the veneration of more uniform voltages for level ing,as by the above arrangement, such variations in the levelling operationare substantially eliminated.

Relay M and switch O do not operate immediately upon the engagement ofcontacts E 147 and the separation of contacts L 130. When approachingthe floor in theup direction, the current flowing through reactanceportion 125 caused a flux to be built up in the reactance in onedirection. Upon the separation of contacts D 120, the current in thereactance and coil O 124 discharged into resistance 145 tending tomaintain the flux built up and, as previously explained, switch O inoperated condition.- Upon the engagement of contacts E 147 and theseparation of contacts L 130 on the overrun, the current supplied tocoils M 131 and O 132 must reverse the flux in the reactance, thustaking a longer time to build up to a value sufficient to cause theoperation of relay M and switch O. Thus contacts N 144, depending fortheir separation upon the operation of relay M, remain closedtemporarily to insure that the current in the generator armature-motorarmature circuit has fallen to a low value. Since the current in theseries field winding may be flowing in a direction such as to cause thegeneration of an E. M. F. which is of proper polarity for operating thecar in the down direction, immediate increase in the strength of theseries field might result in an overrun in the down direction. As thecar returns to the floor, it is stopped by the separation of slow speedlevelling contacts 33 in a manner similar to that described forapproaching the floor.

If the overrun is great enough to cause the engagement of the down fastspeed levelling contacts 35 as well as the down slow speed levellingcontacts 33, resistance 118 is shortcircuited, increasing the generatorvoltage and causing the elevator motor to run at its fast levellingspeed. Further than this, the operation on an overrun is as abovedescribed.

It is to be understood that the operator may control both theacceleration and retardation of the car by moving the car switch insteps. Should the operator suddenly move the car switch from oneposition into the other, for example from up into down position, injuryto the system is prevented by contacts B 65 which remain separated untilthe up direction switch drops out.

In variable voltage control systems of the type wherein the elevatormotor is supplied with current from the generator' of a motor generatorset, the generator is required to opvarying from a maximum yureillustrates the conditions when a small possibility of crate over a widerange of E. M. F. values, in one direction to a maximum in the other.When operating at low values of E. M. F., the armature voltage obtainedfor a given field current may vary over a wide range due to the varyingeffects of residual flux. This effect is very marked under levellingoperatin conditions where low values of generated M. F. are employed.Such low values, of E. M. F. are usually obtained by permitting only asmall amount of current to flow through the generator separately excitedfield winding so as to produce low values of flux. Thus the residualflux present forms a large percentage of the total flux and thereforeaffects the operation of the system very markedly. In order that theeffects of residual flux may be clearly seen, reference may be had totheassumed hysteresis curve shown in Figure 3. This figcurrent is suppliedto the separately excited field winding of a separately excitedgenerator, as during levellingoperation. It will be seen that, for acertain current value, represented by the magnet-izing force Mm, the E.M. F. of the generator may be any value between V1 and V3 depending onthe previous magnetic state of the machine and whether the car isapproaching the floor from one direction or is returning to the floor inthis direction after an overrun from the opposite direction. V2represents the minimum value of the generator E. M. F. for a magnetizingforce Mm of equal but opposite value to magnetizing force Mm. Obviously,such large E.' M. F. variations might result in undesirable variationsin operation under levelling conditions. These variations cannot besatisfactorily corrected by adjusting the amount ot resistance in serieswith the Separately excited field winding. For example, if the amount ofresistance were decreased in order to raise the value of V3, the valueof V1 also would be raised, resulting in an increasing tendency to runpast the floor. Similarly, if the amount of resistance were increased inorder to lower the value of V1, the value of V3 also. would be lowered,with the V3 being of too low a value to return the car to the floorafter an overrun. Thus, if the values of V1 and V3 can be made nearlyequal for levelling operating conditions, the system may be adjusted soas to obtain more uniform operation. This desired result may beattainedby connecting field winding portion 18 to the generator armatureand energizing field winding portion 17.

For convenience of explaining the action of the portions 17 and 18 ofthe field winding, as-- sume that the generator has been in operationwith the portions connected across the mains in such mann-eras to assisteach other and that, as a final step in reducing the generator E. M. F.,both portions are disconnected from the mains and that portion 18 isconnected to the generator armature and portion 17 left unenergized, thepolarity of the connection between the generator armature and portion18y being such that the generator sends current therethrough in adirection to oppose the flux which produces the generator E. M. F. Thefinal values of the generator E. M. F. under such conditions areillustrated in Figure 4, In this figure, the line X-Y is the resistanceline of the field and shows the relation hetween the voltage applied tothe field winding and the number of ampere turns produced thereby. Withthe hysteresis curve, as before, in the first and third angles, the lineX-Y for winding portion 18, in accordance with the polarity ofconnection assumed, is in the second and fourth angles. If both windingportions had been left disconnected, the gen erator E. M. F. would haveassumed a value V@ or V9 depending on the previous polarity of themachine. These values would be due to the residual flux of the generatorfield. For convenience of further explanation, assume that the previouspolarity of the generator corresponded with the polarity indicated by E.M. F. value Vgat the time that Winding portion 17 was disconnected andwinding portion 18 was connected to the armature. It is to be understoodthat the value of the generator E. M. F. at the instant of the change ofconnections would be determined by the time constant of the field andtherefore might be greater than V8. Assuming, however, that thegenerator E. M. F. was at a value V8 at the instant'f change, this E. M.F. applied to winding portion 18 would tend to cause this p portion toexert a magnetizing force of a value M52. Such magnetizing force,however, opposing the flux which produced the armature E. M. F., wouldcause a decreasein the value of the E. M. F. generated. A decreased E.M. F. would simply mean a decrease again in the value of the opposinginagnetizing force. As a result, a state of equilibrium would be reachedwhere any tendency for a decrease in armature E. M. F. -Would result ina decrease in opposing magnetizing force with the consequent increase inarmature E. M. F., i. e., once the armature E. M. F.

is reduced to a value V4, a decrease in value v would mean that theopposing magnetizing force would tend to assume a value Mba, forexample, which would tend to increase the value of the armature E. M. F.The value V5 represents the armature E. M. F. with the state ofequilibrium obtained after a previous armature E. M. F. of the otherpolarity.

According to the preferred arrangement, however, as previouslyexplained, ield winding portion 17 is energized from the mains whenportion 18 is connected to the generator armature. With the windingportions connected in this manner, conditions become as illustrated inFigure 5. In this figure, Mm

represents the magnetizing force created by winding portion 17 with thecar moving in one direction while Mb represents the magnetizing forcecreated by winding portion 18 for the state of equilibrium with the carapproaching the floor in this direction and M61 represents themagnetizing force created by winding port-ion 18 for the state ofequilibrium when the car is being returned to the floor in thisdirection after an overrun from the opposite direction. Graphicall theeffect of the magnetizing force Mm1 o windin portion 17 is to shift theresistance line X for winding portion 18 to the right. When the car isapproaching the floor in this direction, therefore, the final value ofthe armature E. M. F. is that due to the difference in the magnetizingforces of the winding portions, i. e., Mam-Mb, and is represented as V8.W'hen the car is returning to the floor in this direction after anoverrun from the other direction, the nal value of the armature E. M. F.is that due to the difference in the magnetizing .forces of the winding(portions, i.e., Mml-Mbl, and is represente as VT. The armature E. M.F., therefore, lies between the values V8 and V1, which values,relatively speaking, are very nearly equal. Thus the possible range ofvariation 1s much smaller than when an undivided separately excitedfield winding is used as explained in connection with Figure 3. Theincrease in field current to obtain the desired magnetizing force Mm1 ofthe winding portion 17 for the voltages V6 and V1 is effected by theengagement of contacts L 138 in the system described. Any tendency foran increase in the armature E. M. F. under the above describedconditions would result in an increase in the magnetizing force of thewinding portion 18 and thus a decrease in the net magnetizing force, andvice versa.

p It is preferred to utilize the field winding portion 18 to assist thefield winding 17 during car switch operation as described above. Thearrangement of the field winding may be as indicated in Figure 2. Herethe field coils for the north poles are grouped together to be used aswinding portion 17 while the field coils for the south poles are groupedtogether to be used as winding portion 18. lVith the switch L in theposition illustrated, these windings are connected so as to assist eachother, providing alternate north and south poles. The direction of thecurrent is indicated by arrows. The circuit for the field winding may betraced by way of line 74 through winding portion 17 constituting the Npoles, through coil G 75, contacts L 76 and winding portion 18constituting the S poles, to line 89. It is to be understood that themanner of winding is such as to obtain the desired polarity. lVith thewinding of switch L energized by the levelling switch contacts, theswitch is moved into its other position so as to disconnect windingportion 18 from the mains and to connect it to the generator armaturewith the proper polarity. The circuit for winding portion 17 may now betraced by way of line 74 through winding portion 17, by way of line 170through contacts L 134, to line 89. The circuit for winding portion 18may be traced from the lower armature terminal, line 171, a portion ofline 89, by way of line 74 through winding portion 18, by way of line172 through contacts L 135 and resistance 140, series field windings 16,to the upper armature terminal. Lines 173 and 174 indicate theconnection from the generator armature to the motor armature. Thedirection of the current in the generator armature-motor armaturecircuit when the motor is lifting a load is indicated by double arrows.It is to be understood that the manner of winding for the series fieldis such thatV the field due to the series winding assists that due tothe separately excited field winding portions, when the motor is liftinga load. Thus, upon the operation of switch L to cause the engagement ofits contacts L 134 and L 135 and the separation of its contacts L 76,the current supplied to the field winding portion 18 is reversed. Thisis true regardless of whether the elevator motor is lifting or loweringa load since the polarity of the generator armature does not change uponregeneration. The engagement of contacts L 138 results in an increase inmagnetizing force due to the field winding portion 17 as previouslyexplained. Resistance 140, connected in series with the field windingportion 18 when the latter is connected to the generator armature servesto reduce the amount of current supplied to this portion and thereforethe magnetizing force produced thereby, the resistance determining theslope of the line X--Y and therefore the relative values of the armatureE. M. F. Thus it will be seen that, with the above describedarrangement, variations in operation during levelling caused by theeffeet of the residual flux of the generator are substantiallyeliminated. It is to be understood that the above described arrangementis applicable to generators of other pole numbers, a four pole generatorbeing chosen merely for convenience of description. Also it is to beunderstood that the coils of the field windlng might be grouped in otherrelations to effect the desired result.

The series field winding 16 acts to assist the separately excited fieldwinding portions to obtain the desired conditions during operation.Under normal car switch operation, when these winding portions assisteach other, the series field winding acts in the usual manner tocompensate for varying load conditions. During levelling conditions,when the elevator motor is lifting a load, the effect of the seriesfield winding is to aid in bringing the car to the fioor since thecurrent flow in the series field winding is in such direction as toproduce a magnetizing force which assists that due to field windingportion 17 and opposes that due to field winding portion 18. Conversely,when the elevator motor is lowering a load, the effect of the seriesfield winding is to aid in causing the car to stop at the fioor sincethe current flow in the series field winding is in such direction as toproduce a magnetizing force which 0pposes that due to field windingportion 17 and assists that due to field winding portion 18.

Referring again to Figure 1, in order to guard against an open circuitin field winding portion 18 during levelling, with the resultantincrease in generator E. M. F. and therefore car speed when contacts L138 are in engagement, the protective relay J may be employed. Alongwith the employment of relay J, contacts L 136 and L 137 are employed toconnect resistance 15() to the generator armature. The protective relayactuating coil J 151 is connected between a` point on this resistanceand the mid point of field winding portion 18. A bridge circuit is thusformed and is so balanced that under normal levelling operatingconditions, no current flows through coil J 151. However, if an opencircuit occurs in field winding -portion 18 itself or in the circuit forresistance 150, current fiows through coil J 151, causing the operationof the relay. The relay, upon operation, causes the separation ofcontacts J 47 inthe circuit for the actuating coil A 45 of thepotential` switch. Relay J is preferably of the latched type to maintaincontacts J 47 separated, once the relay is operated, until manuallyreset. Switch A, upon dropping out, causes the separation of contacts A50 and A 51. Thus the main field windinor is disconnected from mains 40and 41 and the brake is applied, bringing the motor to a stop. Sincehalf of field winding portion 18 is in each side of the bridge circuit,any transient voltages induced in the winding balance out and do notcause the operation of the protective relay J. However,

. if resistance 140 in one side of the bridge circuit is large, it maybe desirable to divide it into halves, putting one-half in one side ofthe bridge circuit and the other' half in the other side. Suchyarrangement would result in a perfect balance and would insure that`relay J would not be operated under transient voltage conditions.

If desired, the auxiliary protective relay K, preferably of the sametype as relay J so as to maintain its contacts K 48 separated untilmanually reset once the relay has operated, may be employed to protectagainst an accidental open circuit for the coil J 151 and against theaccidental short circuit of resistance E26 during levelling operationwhich would result in an excessive voltage being applied to fieldwinding portion 17. It is to be noted that the auxiliary protectiverelay is provided with two coils K 153 and K 154. Under normal carswitch operating conditions, coil K-153 `is connected in series withcoil J 151 across one-half of field winding portion 18 andrcoil K 154across field winding portion 17. By means of the resistances 155 and15G,.the currentsupplied to the coils ma be adjusted so that the ampereturns .o one coil neutralize those of the other. If the circuit yforcoil J. 151 should be accidentally opened, coil K 154 alone would beenergized, causing the operation of the relay K. Relay K, uponoperation, causes the separation of contacts K 48 in the circuit for thepotential switch actuating coil A 45. Thusv the car is brought to a stopin the manner above described. During the levelling operation, coil K153 is shortcircuited by contacts L 137 so that only coil K '154 isenergized. Coil K 154 is designed, however, so as to causethe operationof the auxiliary protective relay K to effect the stopping of the carwhen an excessive voltage, such as would result from theshort-circuiting of resistance 26, is applied to the coil. The coils ofrelay K are wound with a larger number of turns than coil J f 151 sothat, under normal car switch operation, the current flowing throughcoils K 153 and J 151 does not cause` the operation of relay J.

It is to be noted that, vwhen the car is stopped by deenergizingtheactuating coil of the potential switch or by the centering of the carswitch at such time as to stop the car without the levelling zone, theswitch O is not operated. Thuscontacts O 141 are in engagement, leavingresistance 80 in parallel with resistance 28, and, upon the engagementof contacts H 78, resistance 31 is connected in parallel withresistances 28 and 3() and a so-ft application of the brake is obtained.

As many changescould be made in the above arrangement and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that allInatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative andv not in a limitingsense.

What is claimed is: 1. In combination, a generator having an armatureand a field winding, a source of current, means for connecting the wholeofy said field'winding to said source, and means for reconnecting saidfield winding in such manner that one portion thereof is connected tosaid source and another portion thereof is connected to the armature 'ofthe generator.

2. In combination, a generator having an armature and a field winding,means for driving said generator, a source of current, means forconnecting the whole of said Winding to said source, and means forchanging the connections of said winding so as to have a portion thereofconnected to said source with another portion connected to the generatorarmature.

3. In combination a generator having an armature and a field Winding,means for driving said generator, a source of current, means forconnecting the Whole of said field winding to said source, means forreconnecting said field Winding in such manner that one portion thereofis connected to said source and the other portion thereof is connectedto the generator armature, and means for reducing the voltage ap lied tosaid other ortion of the field winding below that of the generatorarmature.

4. In combination, a generator having an armature and a field Winding,means for driv ing said generator, a source of current, means forconnecting the Whole of said field Winding to said source, means forchanging the connections of said field Winding so as to have a portionthereof connected to said source with another portion connected to thearmature ofthe generator, and means for reducing the voltage applied tosaid other p0rtion of the field Winding below that of the generatorarmature.

5. In combination, a generator having an armature and a field Winding, asource of current, means for connecting the whole of said field windingto said source, a resistance, and means for changing the connections ofsaid field Winding' so as to have a ortion thereof connected to saidsource wit another portion connected in circuit with said resistance tothe armature of the generator.

6. In combination, a generator having an armature and a field Winding,said field wind ing comprising a coil on each field pole, means fordriving said generator, a source of current, and means for connectingcertain of said coils to said source and the remainder of said coils tothe armature of the generator, the manner of connecting said remainingcoils being such thattheir magnetizing force opposes that of saidcertain coils.

7. In combination, a generator having an armature and a field Winding,said field winding comprising a plurality of coils, one on cach fieldpole, a source of current, means for connecting said coils to saidsource, and means for disconnecting alternate coils from said source andconnecting them to the generator armature 8. In combination, a generatorhaving an armature and a field winding, said field winding comprising aplurality of coils, one on each field pole, means for driving saidgenerator, a source of current, means for connecting all of said coilsto said source in such manner as to excite the alternate` poles for likepolarities, and means for disconnecting the coils of alternate polesfrom said source 'and connecting them to the generator arr ture in suchmanner as to reverse the elicit ation of said alternate poles 9. Incombination, a generator having an y armature and a field Winding, saidfield winding comprising a pluralityv of coils, one en each field pole,means for driving said gen erator, a source of current, means forconnecting said coils to said source, means for disconnecting alternatecoils from said source and connecting them to the generator armature,and means for reducing the volt-N a e applied to said alternate coilsIieloiv thai: o the Generator armature 10. Ion combination, a freneratorhavin mi armature and a field Winding, said field 'a ing comprising aplurality of coils, on' each Held pole, means for driving said L erator,a source of current, means for c wg necting all of said coils to saidsource in such manner as to excite the alternate pole; foi,` likepolarities, means for disconnecting the coils of alternate poles fromsaid source anc. connecting them to the generator armat in such manneras to reverse their excitatic and means for reducing the voltage applic.to said coils of alternate poles below that ci: the generator armature.

l1. In combination, a Jenerator having armature and a field Win ing,means for d ing said generator, a source of current, mear for connectingthe whole of-said field Winding` to said source so as to cause thegeneration of r. certain voltage, and means for decreasir" said voltage,said last included means com prising means for connecting a portion saidWinding across said armature.

l2. In combination, a generator having a.;- armature and a fieldWinding, means for di.` ing said generator, a source of current, ysistance, means for connecting the field "rin, ing to said source incircuit with said resance to cause the generation of a certain flotayage, and means for decreasing said voltage` 1j, said last included meanscomprising meaW for connecting a portion of said winding said armatureand for short-circuiting at leas*J a portion of said resistance.

13. In combination, a generator having f armature and a field Winding,means for d ing said generator, a source of current, a resistance, meansfor connecting the field wind ing to said source in circuit with saidres' ance to cause the generation of a certain. vc. age, means forincreasing said voltage, sa third named means comprising means forshort-circuiting said resistance, and means for decreasing said voltage,said last "'Wucf means comprising means for conn` portion of saidWinding to said armut means for short-circuiting :i portion of 'eresistance.

14. In combination, a Generator having an armature and a field Winding,said field Wind- 312e l said resistance, and means for ldecreasing saivoltage, said last included means' compris-` ing means for connectlngcertain of said coils to said armature. and for shortc1rcu1t1ng aportion of said resistance.

15. In combination, a motor, a variable -voltage generator for supplyingcurrent to said motor, said generator having an armature and a fieldwinding, a source of'current, means for causing the motor to run at a.certain speed, said means comprising means for connecting said fieldwinding to said source, and means for causing the motor to run at aslower speed, said last included means comprising means for connecting aportion of said field winding to said armature.

16. In combination, 'a motor, a variable voltage generator for supplyingcurrent to said motor, saidenerator having an armature and a fieldwinding, a source of current, means for causing the motor to runatacertain speed, said means comprising means for connecting said fieldwin ing to said source, and means for causing the motor to run at a a,slower speed, said last included means coml prislng means fordisconnecting av portion of said winding from said source and connectingit to the armature of the generator in such manner as to reverse theflow of current through said ortion.

17. In com ination, a motor, a variable voltage generator for supplyingcurrent to said motor, said enerator having an armature and a fieldwinding, a source of current, .means for causing the motor to run at acertain speed, said means comprisingmeans for connecting said fieldwinding to said source, means for causing said motor to run at a' slowerspeed, said second included means comprising means for disconnecting aportion of said wlnding from said source and connecting it to thearmature of the generator, and means for reducing the voltage applied tosaid portion of the field winding below that of the generator armature.

18. In combination, a Generator havin an armature and a field winding,means for riving said generator, a sourcel of current, means forconnecting one portion of said winding to saidvsource and anotherportion to the generator armature, and means operable upon theoccurrence of an open circuit in said another portion of the winding todisconnect said one portion of said winding from said source.

19. In combination, a enerator havin an armature and a field win ing,means for riv-` ing said generator, a source of current, means forconnecting the whole of said field winding to said source, a resistance,means for reconnecting said field winding in such manner that oneportion thereof is connected to said source in circuit with saidresistance so as to cause the application of a voltage of a. `A

certain value to said portion and another portion thereof isV connectedto the generator armature, and means operable, upon an in crease in thevoltage a plied to said one portion to a value higher han said certainvalue, to disconnect said one portion from said source.

In testimony whereof, I have signed my name to this specification.

LEE I; DAVIS.

